1. Field of the Invention
The present invention relates to an abnormal vibration monitor which detects an abnormal vibration of rotary devices etc. in an explosive atmosphere by piezo-pick-ups and monitors the abnormal vibration.
2. Description of the Prior Art
FIG. 1 is a schematic view of a structure of a detector of a conventional vibration monitor and FIG. 2 is a schematic view of a structure of a conventional vibration monitor.
In FIGS. 1 and 2, the reference numeral (1) designates a pressure durable antiexplosion casing; (2) designates a piezo-acceleration pick-up; (3) an output cable of the pick-up (2); (4) designates a pre-amplifier (a charge amplifier); (5) designates a cable for a power source of the pre-amplifier (4); (6) designates an output cable for the pre-amplifier (4); and (7) designates a monitor-alarm which detects a vibration waveform signal transmitted from the output cable (6) and alarms when an abnormal condition is detected.
The pressure durable antiexplosion casing (1) is equipped with a bearing of a rotary device in an explosive atmosphere. The vibration acceleration caused at the part, is converted to a corresponding voltage by a piezo-acceleration pick-up (2). In order to prevent attenuation of the voltage in low frequency when the output cable is long, the pre-amplifier (4) is connected. The output from the pre-amplifier (4) is transmitted to a monitor-alarm departed from the explosive atmosphere to detect an abnormal vibration.
The monitor having said structure can detect vibrations of rotary devices at a plurality of parts. The pick-up (2) and the pre-amplifier (4) are contained in the pressure durable antiexplosion casing. Even though an abnormal failure is caused in the pre-amplifier (4), the explosion in the atmosphere is prevented. However, this structure requires a plurality of the output cables (6) for connecting the casing (1) to the monitor-alarm (7) whereby a possibility of a failure is increased and a cost for the cables is increased and an instrumental operation and maintenance operation are also increased.